1. Add a line

Ctl+Alt+Up/Down
command: select_lines
args: forward [up:false, down:true]

2. Split selection into lines

Ctrl+Shift+L for a selected block
command: split_selection_into_lines

3. Add next occurrence

Ctrl+D
command: find_under_expand

4. Find all occurrences

Alt+F3
command: find_all_under

5. Undo add line/occurrence

Ctrl+U
command: soft_undo

6. Add with mouse

Ctrl+Mouse click
source: Default.sublime-mousemap

7. Add/Remove custom blocks to selection

Ctrl+DragSelect - add to selection
Alt+DragSelect - remove from selection
source: Default.sublime-mousemap

8. Create/Add/Remove selection by columns

Shift+MouseRight+DragSelect - create selection
Ctrl+Shift+MouseRight+DragSelect - add to selection
Alt+Shift+MouseRight+DragSelect - remove from selection

[Ctrl|Alt]+MouseWheel+DragSelect - the same actions

source: Default.sublime-mousemap